1. Field of the Invention
The invention relates to a substrate support chuck within a semiconductor processing system. More particularly, the invention relates to a stand-off pad disposed upon the surface of a substrate support chuck for supporting a semiconductor wafer such that the surface of the wafer that faces the chuck is spaced-apart and substantially parallel to the surface of the chuck.
2. Description of the Background Art
Substrate support chucks are widely used to support substrates within a semiconductor processing system. A particular type of chuck used in high-temperature semiconductor processing systems, such as high-temperature physical vapor deposition (PVD), is a ceramic electrostatic chuck. These chucks are used to retain semiconductor wafers, or other workpieces, in a stationary position during processing. Such electrostatic chucks contain one or more electrodes imbedded within a ceramic chuck body. The ceramic material is typically aluminum-nitride or alumina doped with a metal oxide such as titanium oxide (TiO.sub.2) or some other ceramic material with similar resistive properties. This form of ceramic is partially conductive at high temperatures.
In use, a wafer rests flush against the surface of the chuck body as a chucking voltage is applied to the electrodes. Because of the conductive nature of the ceramic material at high temperatures, the wafer is primarily retained against the ceramic support by the Johnsen-Rahbek effect. Such a chuck is disclosed in U.S. Pat. No. 5,117,121 issued May 26, 1992.
One disadvantage of using a chuck body fabricated from ceramic is that, during manufacture of the support, the ceramic material is "lapped" to produce a relatively smooth surface. Such lapping produces particles that adhere to the surface of the support. These particles are very difficult to completely remove from the surface. Additionally, the lapping process may fracture the surface of the chuck body. Consequently, as the chuck is used, particles are continuously produced by these fractures. Also, during wafer processing, the ceramic material can abrade the wafer oxide from the underside of the wafer resulting in further introduction of particulate contaminants to the process environment. During use of the chuck, the particles can adhere themselves to the underside of the wafer and be carried to other process chambers or cause defects in the circuitry fabricated upon the wafer. It has been found that tens of thousands of contaminant particles may be found on the backside of a given wafer after retention upon a ceramic electrostatic chuck.
Japanese Patent Application No. 60-261377, published Dec. 24, 1985, discloses a ceramic electrostatic chuck having an embossed support surface. The embossing reduces the surface area of the ceramic support that contacts the wafer. Consequently, the number of contaminant particles transferred to the wafer is reduced. However, such an embossed surface maintains some degree of contact between the ceramic material and the underside of the wafer. Thus, contamination, though reduced, is still substantial.
Similarly, substrate support chucks that are used in low-temperature processing (e.g., less than 300 degrees Celsius) may also produce contaminant particles that interfere with wafer processing. Such low-temperature chucks include electrostatic chucks and mechanical clamping chucks which contain wafer support surfaces that are typically fabricated from dielectric materials such as alumina. These types of chucks have also been found to produce particulate contaminants that can adhere to the underside of the wafer during processing.
Therefore, a need exists in the art for an apparatus that reduces the amount of contaminant particles that adhere to the underside of the wafer while supported upon a chuck.